[OilValleyRy]

I would (also) suggest either an IR beam sensor or maybe motion sensor.
The + with good old fashioned IR beamers is they work even in night ops. The only trick is to put the projector and receiver at an angle, not straight across, so they don’t catch the gaps between cars. Easily hidden in ROW electrical cabinets, bushes, made to look like a relay box for signals, etc.
The motion sensor (as found in hand dryers, security lights, etc) might be too big. But that would probably work in night ops too because they don’t require ample lighting.

 

[OilValleyRy]

I saw a circuit board using these sensors, angled as you suggested however the circuit boards were quite pricy.
If you have any links to a cost effective option, I would be interested to see.

I would look at Circuitron and similar companies. I don’t have a Walthers catalog anymore so I can’t say who else makes them. But you really just need a flashing circuit with a timer that has solder points for inputs of your choosing. The timer should (should!) start counting when the beam is no longer broken. So… unbroken beam has no crossing lights, break the beam & lights flash, beam restored and lights keep flashing until timer finishes.
The circuit in that Bachmann(?) kit shown in your photos probably has the flashing circuit with no timer, which you probably… should be able to add on as a secondary board. Uhhm, think that would be on the output side (crossing lights lead side)?? Dam, my dad is so much better at this stuff than I am. You could just make it easy on yourself and wire everything into a Fanuc. Wire it once then play around with inputs and outputs for 10 years. Lol But I’m preaching to the choir. If you need Fanuc components I know a guy (relation) who can likely get whatever you need.

 

[OilValleyRy]

I never had any problem from lighting on a tv remote. I guess it’s possible. Just never had the sun turn on a television. A constant beam that triggers the bells & whistles when interrupted is the time tested method. Plenty of articles on ways of doing it. That’s how I’ll do mine, old reliable, like #5s.

 

[OilValleyRy]

tv remotes use a signal modulated at a specific frequency which receivers are tuned for and use automatic gain control to distinguish the modulated signal from background

Half of that was Greek lol but I know it means less unwanted interference. And I like that.